The present invention relates in general to an electronic transmitter and receiver system involving a multi channel transmitter of extremely low power consumption and compact size, capable of fitting in the palm of the hand, which is completely portable and capable of high fidelity stereo radio transmission, and a separate receiver to be linked by radiant energy transmission with the transmitter for demodulating the transmitted signal, decoding, and driving at least two channels of amplification.
The transmitter and receiver system of the present invention has particular application to audio frequency processing for electrical musical instruments at the instrument. As a specific example, the palm size stereo transmitter may be provided with two audio processing channels to provide stereo pickups from a guitar or other musical instrument or pickups from two microphones receiving sound from a musical instrument, and which provides radio transmission of the two channels as high fidelity stereo radio signals to the receiving device. The receiving device is capable of demodulating the transmitted signal, decoding the stereo multiplex modulation, and driving two channels of amplification to provide a high fidelity stero amplified audio output.
The extremely low power consumption and compact character of the transmitting device provides audio frequency processing for electrical musical instruments at the instrument, by a radio linked system with the receiver, amplifier, permitting removal of the umbilical cord customarily provided between the musical instrument and its amplifier. This allows a degree of freedom long enjoyed by the more classical acoustical instruments, but not available in the field of electrical musical instruments heretofore.
In general, the transmitter comprises a pair of amplifiers forming audio processing circuitry which provides selection between one mode of undistorted amplification, one mode of odd harmonic generation, and one mode of even harmonic generation. Provision is made for more than one input per channel. A doublesideband suppressed carrier signal is formed from the output of an oscillator and the difference between the signals in the two channels, is combined with signals from the two channels and a pilot signal. This combination is employed to modulate a voltage controlled oscillator whose center frequency is the carrier frequency, to provide the signal radiated from the antenna to the receiver. The receiver includes an amplifier which receives the signal from its associated antenna, amplifies it to the limiting input level of a demodulator, and the stereo composite signal of the demodulator is decoded by an amplifier which provides two distinct channels of high fidelity audio signals capable of driving a standard stereo amplifier.
By the judicious circuit design, an extremely compact portable small size high fidelity stereo transmitter is provided capable of being carried by the musical instrument or by the instrumentalist, for example, in his pocket, and operated for reasonable periods of time, to provide high fidelity stereo amplification through a radio link to a stereo amplifier without requiring direct mechanical or electrical connection between the instrument and the amplifier.